Unit dose (also called single dose) detergent products are often found by some consumers to be preferable for use in automatic dishwashing and laundry applications. Unit dose products have several advantages, including convenience of use and dispensing, lower cost per use, and avoiding or minimizing skin contact with potentially irritating cleaning compositions.
Unit dose detergent products often employs polyvinyl alcohol (PVOH) or polyvinyl acetate (PVA) films to form a sealed container (pac or pack), optionally with multi-compartments, for storing detergent compositions. The detergent compositions may include surfactants and other ingredients commonly used in a detergent formulation, as well as water, glycerin, and propylene glycol to form a liquid carrier. Glycerin and propylene glycol are typically used in an amount sufficient to bind water, solvate materials, and fill volume within the detergent pack. The detergent compositions may be in a liquid form.
In unit dose detergent products currently on the market, efflorescence may be observed. Efflorescence is a phenomenon when solvated salts in a liquid formulation precipitate out, on, or in the PVOH films of unit dose detergent products. Typical drivers of efflorescence include sodium ions, sulfite ions, sulfate ions, calcium ions, and interactions of ionic liquids in a detergent formulation. Efflorescence may occur at elevated temperatures, room temperatures, or both. But it is generally more severe at high temperatures. It may also occur within weeks or several months, depending on the formula composition. Efflorescence is most easily observed when the unit dose pacs have a detergent composition in the form of a solution and a gel. It is less noticeable when the detergent composition is in the form of a paste or a suspension. Efflorescence affects the aesthetic appearance of unit dose pacs. It may also negatively impact the pac's ability to dissolve in water, thus potentially lowering its cleaning performance in the wash drum. The occurrence of efflorescence in unit dose detergent pacs is often considered by consumers as an indication that the unit pacs have turned bad and cannot be used.
The efflorescence problem may be more serious when liquid detergent products include anionic surfactants having a sulfate group. Such surfactants, if undiluted, are usually in a light yellow color, due to impurities resulting from sulfation. Unit dose pacs including such surfactants, in a diluted concentration, are more prone to turning yellowish over time, depending on the formula composition in the pacs and the storage conditions. One way to reduce yellowing of the detergent solution is to add a whitening/brightening agent and/or a yellow color reducing agent to the formulation. However, because a whitening/brightening agent and a reducing agent often contain cations and ions, the addition of these agents to the detergent solution may aggravate the efflorescence issue.
There is a need in the art for improved detergent formulations which can effectively suppress efflorescence while maintaining high detersive performances. It is desirable that products made from the improved detergent formulations are free of efflorescence over the entire product shelf life under the typical shipping and storage conditions. It is also desirable that the improved detergent formulations are composed of cost effective and preferably, green raw materials. Other desirable features and characteristics of the detergent formulations and unit dose products in accordance with the present invention will become apparent from the subsequent detailed description of the invention and the appended claims.